Time resolved Raman spectroscopy for depth analysis of multi - layered mineral samples Chapter 3 3

Time Resolved Raman Spectroscopy (TRRS) can provide subsurface information from multi-layered samples of transparent and translucent evaporative and silicate minerals up to several cm thick. Depth information was obtained using 3-ps pulsed laser excitation at 720 nm and a gated intensified CCD detector with stepwise increasing delay times. Blocks of different minerals were used as first, second or third layers and Raman spectra from deeper layers could be detected through 10 mm of translucent calcite and up to 40 mm of transparent halite crystals. Measurements by conventional confocal Raman, as well as Spatially Offset Raman Spectroscopy (SORS) were also successful in distinguishing different mineral layers. This study establishes the great potential for the use of Raman spectroscopy in future planetary exploration, where TRRS could be used as a non-invasive tool for profiling the (sub-)surface at millimetredepth resolution.